This invention relates to fuzes for use with line charges and other ordnance items. In particular, this invention relates to fuzes that will enable, arm, and fire on command using magneto-inductive signals that are propagated at extremely low frequencies (ELF) to very low frequencies (VLF).
Using explosive weapon systems for a wide variety of commercial and military purposes usually requires considerable logistics and planning efforts to get the job done safely and effectively. Devices are required that will reduce the weight and space allocated to fuzing in ordnance and provide a safe and reliable arm-and-fire capability on-command. This requirement becomes especially important where assault or breaching operations occur in the littoral regions of the world. In other words, better fuzes and similar devices are needed for line charge systems and other weapon systems that are intended to be deployed in support of military and civilian operations.
For example, one effective line charge is the Shallow Water Assault Breaching System (SABRE), EX9 MODO. SABRE is launched via rocket. Only after the line charge is picked up does the fuzing become airborne and begin to become functional. SABRE requires a fuze that is able to function safely and reliably in accordance with established design criteria and under all operational conditions; however, the designed capabilities of the current SABRE fuze are compromised. This is because the rocket does not throw the line charge very far from the launch craft, and it is the fuze which provides for enabling, arming, and firing of the SABRE line charge. Because the line charge is very long (350 feet) and because SABRE will be used under circumstances for which warheads will not be under water, the fuze is prone to failing to meet crucial safety requirements.
One of these crucial safety requirements is set by MIL-STD-1316 and reads "no fuze shall arm prior to reaching safe separation." Safe separation is defined as the distance from the launch craft at which detonation of the ordnance will not result in unacceptable damage to the host craft or unacceptable injury to its occupants. The sensing of this safe separation distance is not a trivial concern. Fuzing that relies on a time delay element alone or in combination with a water sensor to delay arming (pyrotechnic, electronic, or mechanical), does not sense distance. Such fuzing does not limit the potential for the catastrophic consequences which are associated with deployment of an explosive line charge. The line charge may enable the current fuze (committing it to fire) while a section of the high explosive line charge remains out of the water or too close to the host platform. The probability of such a disastrous event must not exceed one instance out of one million munition deployments, without violating the requirement imposed by MIL-STD-1316 for safe separation.
Some fuzes for explosive line charges and similar explosive weapon systems use lanyards. At launch and subsequent fuze lift off of a line charge, a lanyard, tethered to the fuze, begins to pay out. The length of the lanyard is measured to ensure a safe separation distance. When the fuze flies far enough to pay out the measured length, the lanyard pulls tautly and exerts a tensile force on the fuze. This tensile force moves fuze explosive components to an in-line position to arm the fuze. The arming force also activates delay elements (pyrotechnic, electronic, or mechanical) that delay fuze detonation or arming until the ordnance has traveled to its predicted destination.
Unfortunately, fuzes employing lanyards are inherently unreliable at sensing a safe separation distance so that the fuze may be armed before the safe separation distance actually has been reached. Lanyards can snag, knot, fray and become entangled to shorten their apparent length to cause premature function, arming, or firing before the desired separation distance is reached. Also, lanyards can entangle items on the host craft to result in catastrophic failure when the entangled ordnance is detonated. Lanyards also increase the possibility of damage to the ordnance or launch craft by entraining a foreign object also known as FOD damage.
Lock-out timers have been added to lanyard systems. The lock-out timers usually pin the arming mechanism in place until a set time has elapsed after launch. This precludes sensing any premature arming force prior to the opening of the arming window. However, the problem with this arrangement is that it trades safety for reliability and it uses time as an indication of man-weapon separation distance rather than a direct measurement or discriminator.
RF commanded fuzes, water sensing fuzes, or acoustic fuzes have been used but each has inherent limitations especially when they are used to fuze a 350 foot long warhead. When launched into a mine/obstacle laden field during an amphibious assault, fuzes that sense water have limited operational viability since they may lodge atop an obstacle out of the water and dud. On the other hand, RF commanded fuzes are reliable on top of the beach or hanging in the air. But, if the RF fuzes are under water, earth, sand or vegetation, the RF command signals may not penetrate to the fuzes and the interconnected line charges will be duds. This limitation is partially corrected by using floating antennas for the RF commanded fuzes to have any chance of working in marine environments. However, floating antennas are inherently unreliable because they are prone to breakage, entanglement, or sinking. In addition, they are susceptible to electromagnetic pulse and exploitation by electronic warfare countermeasures. In general, RF commanded fuzes have very limited usefulness in the very hostile and RF saturated environment during amphibious assault operations.
Acoustic fuzes also are limited because they cannot effectively be communicated to in the air or, for that matter, when they are in the water due to the deleterious effects of sediments, microorganisms, algae, changes in salinity, multipaths, thermoclines, and biotic-induced noise and interference. Acoustic fuzes are unreliable at detecting signals in the littoral regions near amphibious assaults when noise is radiated through the water from ambient ships, mammals, munitions, landing craft, sonar, and crashing surf.
Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for fuzes that eliminate the aforestated problems of the prior art by having unidirectional or bidirectional communications using magneto-inductive transmitters and receivers operating in the ELF to VLF range to assure safe and reliable commands and confirmations to effect on-command arming and subsequent detonation from a safe man-weapon separation distance of weapons emplaced in the littoral battle space. In addition, this fuze may be used (communicated to) one-way and still provide for safe and reliable functioning for a number of military and civilian items.